Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

399
FXUS63 KLOT 122339
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
639 PM CDT Fri Jun 12 2026

.KEY MESSAGES...

- Thunderstorms are likely Saturday evening into early Sunday
  morning. A few storms could be strong to severe, with a threat
  for large hail, damaging winds, and locally heavy rainfall.

- Cooler temperatures (highs in the 70s to low 80s) along with a
  returning threat for showers and thunderstorms is expected for
  early to midweek.

&&

.DISCUSSION...
Issued at 300 PM CDT Fri Jun 12 2026

Temperatures remain in the upper 70s across the area this
afternoon, in the wake of yesterday`s frontal passage. This
front has also pushed the richer surface dewpoints well off to
the east, with dewpoints in the middle to upper 50s today.

By tonight, surface high pressure anchored over southern Indiana
will begin to move off to the east, with southwesterly flow
establishing across the local area prior to sunrise. As deep
surface low pressure begins to eject across northern Ontario by
tomorrow afternoon, a trailing cold front will begin to move
southeast across the upper Midwest. Ahead of this front, the
increasing southwesterly flow will bring a return of richer
surface dewpoints in the upper 60s into northern Illinois and
northwest Indiana. Though mid-level lapse rate are not overly
steep (6-6.5 C/km) the increasing surface moisture should
promote MLCAPE increasing to ~2000-2500 J/kg immediately ahead
of the cold front.

As an upper shortwave ejects southeast across the northern
Plains tomorrow evening, middle and upper flow strengthens
enough to promote ~30-35kts of effective shear. The stronger
westerlies aloft lag the front somewhat, and keeps the strongest
shear largely postfrontal tomorrow. Still, increasing
convergence along the surface front is expected to lead to
widespread thunderstorm development across central and eastern
Iowa by late tomorrow afternoon. It is expected that this will
move east and southeast with time, and impact much of northern
Illinois and northwest Indiana late tomorrow evening and
overnight. Uncertainty remains with respect to the threat for
severe weather, with a consensus among high-res guidance of
quick upscale growth along the surface front. The propagation of
any clusters and the development of cold pools will likely drive
the threat locally, and lends low confidence for now in the
coverage of any severe threat. This is in line with the latest
SPC Day 2 outlook, with the slight risk trimmed to the southwest
and now is restricted to the western half of Illinois. Any
thunderstorms should quickly exit the area after midnight, as
the cold front begins to clear the area off to the southeast.

The passage of this front will usher in cooler temperatures as
we head into early next week, with highs remaining in the middle
70s to low 80s each afternoon. Deep upper troughing remains
anchored over northern Ontario through much of the upcoming
week, promoting broad northwest flow across the Midwest into the
Ohio Valley. This suggests the threat for showers and
thunderstorms will persist into much of early to middle week
across the area. Any threat for severe weather is less certain,
with the cooler temperatures keeping instability more limited.

Brown - WFO LSX

&&

.AVIATION /00Z TAFS THROUGH 06Z SUNDAY/...
Issued at 639 PM CDT Fri Jun 12 2026

Aviation forecast concerns for the 00Z TAFs:

- Low confidence in timing/coverage of scattered TSRA late
  Saturday/Saturday evening.

Quiet, VFR weather conditions are expected through at least
midday Saturday. Breezy west winds will diminish to less than
10 kts and turn southwest with sunset this evening. Winds will
pick up again after sunrise Saturday morning, becoming gusty
20-25 kts again especially by afternoon.

A cold front will slowly approach the area from the northwest
Saturday afternoon and evening, eventually pushing through the
terminals sometime Saturday evening/overnight, though there is
some spread within current model guidance as to the exact
timing. In addition to timing differences with the front, there
is quite a spread in various high-res guidance on scattered
thunderstorm timing and coverage head of the front. While some
guidance brings storms into the terminals as early as ~20Z
Saturday afternoon, high-res ensemble guidance suggests somewhat
later timing (23-00Z onward) for higher probability(40-55%) of
TSRA. Given the low confidence in individual models/runs have
trended toward the ensemble mean timing with PROB30 mentions
after 23Z for RFD and 00Z for the Chicago metro terminals. May
eventually end up needing TEMPO or prevailing mention for a
time, though confidence is too low at this time.

Otherwise, VFR conditions are expected through the period,
other than possible brief IFR/MVFR in TSRA.

Ratzer

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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